Method of Preparing a Material for an Artificial Seed

ABSTRACT

A method of preparing a material for use in a manufactured seed is provided. The method includes providing the material having a melting temperature. The method also includes subjecting the material to a heat treatment at a temperature about 10% below the melting temperature for a predetermined period of time.

BACKGROUND

Asexual propagation of plants has been shown for some species to yieldlarge numbers of genetically identical embryos, each having a capacityto develop into a normal plant. Such embryos are usually furthercultured under laboratory conditions until they reach an autotrophic“seedling” state characterized by an ability to produce its own food viaphotosynthesis, resist desiccation, produce roots able to penetratesoil, and fend off soil microorganisms. Some researchers haveexperimented with the production of artificial seeds, known asmanufactured seeds, in which individual plant somatic or zygotic embryosare encapsulated in a seed coat. Examples of such manufactured seeds aredisclosed in U.S. Pat. No. 5,701,699, issued to Carlson et al., thedisclosure of which is hereby expressly incorporated by reference.

Typical manufactured seeds include a seed shell, synthetic gametophyteand a plant embryo. A manufactured seed that does not include the plantembryo is known in the art as a “seed blank.” The seed blank typicallyis a cylindrical capsule having a closed end and an open end. Thesynthetic gametophyte is placed within the seed shell to substantiallyfill the interior of the seed shell. A longitudinally extending hardporous insert, known as a cotyledon restraint, may be centrally locatedwithin one end of the seed shell, surrounded by the syntheticgametophyte, and includes a centrally located cavity extending partiallythrough the length of the cotyledon restraint.

The cavity is sized to receive the plant embryo therein. The well-knownplant embryo includes a radicle end and a cotyledon end. The plantembryo is deposited within the cavity of the cotyledon restraint,cotyledon end first. The plant embryo is then sealed within the seedblank by an end seal. There is a weakened spot in the end seal to allowthe radicle end of the plant embryo to penetrate the end seal.

At has been discovered by the inventors of the present, method that thetale of normal germination of an embryo from such manufactured seeds wasunacceptably low. Their analysis noted that only about 42% of embryoswithin a study group of manufactured seeds produced a normal seedlinghaving an expected root, cotyledons, etc. The present inventorsconcluded that although existing methods of preparing seed shells havebeneficial aspects, they are not without their problems. Thus, there isa need for a method of preparing a material for use in a manufacturedseed that improves the productivity of the manufactured seed.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

A method of preparing a material for use in a manufactured seed isprovided. The method includes providing the material having a meltingtemperature. The method also includes subjecting the material to a heattreatment at a temperature about 10% below the melting temperature for apredetermined period of time.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional side planar view of an artificial seed.

DETAILED DESCRIPTION

Methods of preparing a material for use in a manufactured seed may bebest understood by first understanding components of a manufacturedseed. In that regard, and with reference to FIG. 17 such a manufacturedseed 20 includes a cylcap 22, a seed shell 24, nutritive media 26, suchas a gametophyte, and a dead end seal 28. The seed shell 24 is suitablyformed from a section of tubular material. In one embodiment, the seedshell 24 is a sectioned straw of fibrous material, such as paper. Thesections of straw may be pre-treated in a suitable coating material,such as wax.

In other embodiments, the seed shell 24 is formed from a tubular sectionof biodegradable, plastic material. One such material is a utilizedpolylatic acid (“PLA”) and is sold by NAT-UR of Los Angeles, Calif.Another material within the scope of the disclosure is apolycaprolactone (“PCL”) mixture, such as Dow Tone P-787 (Dow ChemicalCo., Midland, Mich. 48647) with a 1% Tegomer H SI6440 plasticizer(Degussa Goldschmidt Chemical Corp, 914 East Randolph Road, Hopewell,Va. 23860).

Such biodegradable plastic tubes are sectioned into appropriate lengthsfor a manufactured seed. Further, such biodegradable plastic tubes mayor may not require a wax coating as such tubes are already resistive toenvironmental elements. It should be apparent that although sectioningtubes is preferred, other embodiments, such as obtaining tubes ofappropriate size for use as manufactured seeds, are also within thescope of the present disclosure.

The cylcap 22, also known as a restraint, is suitably manufactured froma porous material having a hardness strong enough to resist puncture orfracture by a germinating embryo, such as a ceramic or porcelainmaterial, and includes an end seal portion 30 and a cotyledon restraintportion 32. The cotyledon restraint portion 32 is suitably integrally orunitarily formed with the end seal portion 30. The cylcap 22 alsoincludes a longitudinally extending cavity 34 extending through the endseal portion 30 and partially through one end of cotyledon restraintportion 32. The open end of the cavity 34 is known as a cotyledonrestraint opening 36. The cavity 34 is sized to receive a plant embryo42 therein.

In certain embodiments, as the cylcap 22 is suitably manufactured from aporous material, it may be desirable to coat the cylcap 22 with abarrier material to reduce the rate of water loss and restrict or reducemicrobial entry. Such barriers include wax, polyurethane, glaze, nailpolish, and a coating sold by H. B. Fuller of Minneapolis, Minn. underthe product name PD124.

The end seal portion 30 is suitably circular when viewed in a top planarview and includes sidewalls 38. Although circular is the preferredembodiment of the end seal portion 30, other embodiments and shapes,such as polygonal, square, triangular, oval and other shapes, are alsowithin the scope, of the present disclosure.

In the embodiment of FIG. 1, the sidewalls 38 are defined by thethickness of the end seal portion 30 and has a diameter substantiallyequal to the inside diameter of the seed shell 24. In certainembodiments, the cylcap 22 is bonded to the seed shell 24 by heat. As itnon-limiting example, during manufacturing, the cylcap 22 may be heatedto a predetermined temperature, such that when the seed shell 24 and thecylcap 22 are co-joined, heat transferred, between the cylcap 22 and theseed shell 24 causes either the seed shell 24, the cylcap 22, or both tomelt, thereby bonding the two together. In other embodiments, the cylcap22 and the primary end seal 44 are first heat welded, then in a separatestep the combined primary end seal-cylcap is reheated and the seed shell24 is also heated and the two are joined. Other methods of bonding thecylcap 22 to the seed shell 24, such as a wax bond or a hot glue melt,are also within the scope of the present disclosure.

The sidewalls 38 may include a tapered portion 40. The tapered portion40 may be a chamfer of one end of the end seal portion 30. The taperedportion 40 assists in assembling the cylcap 22 to the seed coal 24during manufacturing. Although a tapered portion 40 is preferred, otherembodiments, such as a cylcap that does not include a tapered portion,are also within the scope of the present disclosure. An embryo 42 isdisposed within the cavity 34 and is suitably sealed therein by a liveend seal 43.

The live end seal 43 includes a primary end seal 44 and a secondary endseal 21. The primary end seal 44 is suitably formed from a PCL materialdescribed above and includes a centrally located opening 50. The opening50 is sized to correspond to diameter of the cavity 34 of the cylcap 22to permit a germinating embryo 42 to pass therethrough. The primary endseal 44 is suitably attached to the end seal portion 30 by a variety ofmethods, including glue or heal bonding.

As a non-limiting example, the primary end seal 44 is mated to apre-healed cylcap 22, such that the opening 50 is located above thecavity 34. The heal welds or bonds the primary end seal 44 to the cylcap22. It should be apparent that the primary end seal 44 may be attachedto the cylcap 22 before or after the cylcap 22 is attached to the seedshell 24. Also, if the seed shell 24 is constructed from PCL, it isdesirable but not necessary that the melt temperature of the primary endseal 44 and the seed shell 24 be similar.

As another non-limiting example of attaching the primary end seal 44 tothe cylcap 22, includes an adhesive gasket. In this example, the primaryend seal 44 is heat sealed or bonded to the cylcap 22 with the opening50 co-axially aligned with the cavity 34. In this process, a form isused to bend edges of the primary end seal 44 around the perimeter ofthe end seal portion 30 of the cylcap 22. If the melt temperature of theprimary end seal 44 and the seed shell 24 are different, then a lowbloom cyanoacrylate is used as an adhesive gasket to bond the primaryend seal 44 and the seed shell 22.

Heat is applied after the glue and is done so as to thin the glue sealby melting incongruities that typically occur when manufacturing theseed shell 24 and forming the adhesive joint. Thereafter, the cylcap 22,including the primary end seal 44, is attached to the seed shell 24. Asnoted above, this method is also suitable to a cylcap 22 that is alreadyattached to the seed shell 24. Finally, the foregoing method ofattaching a primary end seal 44 to a seed shell 24 may be used for heatweld compatible or incompatible materials.

The secondary end seal 21 will now be described in greater detail. Inthat regard, the secondary end seal 21 is suitably formed from awell-known sealing material, such as Parafilm®. The secondary end seal21 is formed and attached to the primary end seal 44 by a well-knownmethod, such as heat bonding or gluing. In some embodiments, a sealingwax may be used to facilitate bonding between the PCL and the Parafilm.The secondary end seal 21 also includes a predetermined burst strengthto permit a germinating embryo 42 to penetrate through the live end seal44.

Still referring to FIG. 1, the tertiary seal 60 will now be described ingreater detail. The tertiary seal 60 and live end seal 43, as used inthe present embodiment, define an outer sealing layer and an innersealing layer, respectively. Although the live end seal 43 has beendescribed as including both a primary end seal 44 and a second end seal21, it should be apparent that the disclosure is not intended to be solimited. As a non-limiting example, the live end seal 43 may includeonly the secondary end seal 21 and, therefore, such embodiments are alsowithin the scope of the present disclosure.

The combination of the tertiary seal 60 and live end seal 43 creates asealing surface, wherein the sealing layer, defined by the tertiary seal60, is made from a predetermined material that degrades in structuralintegrity after a predetermined exposure to environmental conditions.The tertiary seal 60 also serves as an anti-microbial sealant to sealand protect around the embryo as the embryo germinates and emerges fromwithin the seed shell 24 and protects the cotyledon restraint cavity.Suitable materials used to manufacture the tertiary seal 60 includewater soluble materials, wax, environmentally degradable materials, andbiodegradable materials. Thus, such materials, as well as materialsequivalent in structure and properties, are within the scope of thepresent disclosure.

As noted above, the seed shell 24 and primary end seal 44 are suitablyformed from a polyester material, such as biodegradable plastic. Onemethod of preparing the material for use in making components, such asthe seed shell 24 and primary end seal 44, of the manufactured seed 20in accordance with the present disclosure includes obtaining strips ofmaterial, such as strips of plastic. Such plastics within, the scope ofthe appended claims includes biodegradable plastics, such as PCL.

The strips of material are annealed using well-known annealing methodsto improve dimensional stability. In one non-limiting example, strips ofPCL are annealed at a temperature of about 63° C. for a range of timesubstantially between 35 minutes and 90 minutes. In one embodiment, thestrips of PCL are annealed for 45 minutes. The annealing time is a timesufficient to render the strips of PCL dimensionally stable during heatwelding. Thus, it should be apparent that the temperature and timerequired for annealing is a function of the material and is within thescope of one in the art. Further, it should be apparent that the stripof material need not be annealed. Such embodiments are also within thescope of the appended claims.

The strips of material, regardless if they have been annealed, are heattreated to remove toxins. In this process, and for PCL, the strips ofmaterial are placed in an oven and heat treated at a temperature ofabout 55° C. for a period of eight days. It should be apparent thatalthough heat treating the material at the specified temperature for thespecific time period, it should be apparent that other temperatures andtimes are within the scope of the present disclosure. As a non-limitingexample, the strips of material may be heated treated at a temperaturethat is approximately 10% below the melting temperature of the material.Further, the time for the heat treatment may be as little as a fewhours. Thus, such times and temperatures are also within the scope ofthe appended claims.

The heat treated strips of material are also subjected to asterilization process. In this process, the strips of material aresubmerged into a sterilization bath of bleach mixture for asterilization soak period. One bleach mixture is 10% bleach and 90%water. The sterilization soak period ranges substantially between 10minutes and 40 minutes. In one non-limiting embodiment, the strips ofmaterial are soaked in the bleach mixture for a sterilization period of30 minutes. After the sterilization soak period, the strips of materialare subjected to a rinse period in deionized water. The rinse period canlast up and beyond 72 hours. Thereafter, the strips of material are airdry in sterile air to evaporate fluids. Finally, the strips of materialare processed to make various components of the manufactured seed 20,such as the seed shell 24 and primary end seal 44.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the invention.

1. A method of preparing a material for use in a manufactured seed, themethod comprising: (a) providing the material having a meltingtemperature; and (b) subjecting the material to a heat treatment at atemperature about 10% below the melting temperature for a predeterminedperiod of time.
 2. The method of claim 1, further comprising annealingthe material at a predetermined temperature below the meltingtemperature.
 3. The method of Claim 1, further comprising sterilizingthe material for a predetermined sterilization soak period.
 4. Themethod of Claim 3, wherein the sterilization soak period issubstantially 30 minutes.
 5. The method of Claim 3, further comprisingdrying the material.
 6. The method of Claim 5, wherein the material is aplastic.
 7. The method of Claim 6, wherein the material is abiodegradable plastic.
 8. The method of Claim 1, wherein the material isa plastic.
 9. The method of Claim 8, wherein the material isbiodegradable.
 10. The method of Claim 9, wherein the predeterminedperiod of time is a range substantially between one and eight days. 11.The method of Claim 9, wherein the predetermined period of time is arange substantially between one and eight days.
 12. A method ofpreparing a material for use in a manufactured seed, the methodcomprising: (a) providing the material having a melting temperature; (b)heat treating the material at a temperature of about 55° C. for a rangeof time substantially between one day and eight days.
 13. The method ofClaim 12, further comprising annealing the material at a predeterminedtemperature below the melting temperature.
 14. The method of Claim 12,further comprising sterilizing the material for a predeterminedsterilization soak period.
 15. The method of Claim 14, wherein thesterilization soak period is substantially 30 minutes.
 16. The method ofClaim 14, further comprising drying the material.
 17. The method ofClaim 16, wherein the material is a plastic.
 18. The method of Claim 17,wherein the material is a biodegradable plastic.
 19. The method of Claim12, wherein the material is a plastic.